Process for transmitting data packets of predefinable priority classes using ethernet from a first device to at least one other device

ABSTRACT

In the method, at least one timing message is generated by a first arrangement at predefinable time intervals and is transmitted to at least a second arrangement. The timing message contains a synchronization method, as a function of which time intervals which are provided for the transmission of data packets (DP) each having a predefinable priority class are determined. After reception of the timing message, the received timing message is evaluated, a synchronization time being determined, as a function of which the time intervals which are provided for the transmission of data packets each having a predefinable priority class are determined.

BACKGROUND OF THE INVENTION

Local computer networks which are configured according to the IEEE 802.3Standard, which is referred to below as Ethernet Standard, constitute atechnology with which terminals are connected via a commonly used,serial bus. The access to this bus is regulated by means of theso-called Carrier Sense Multiple Access/Collision Detection (CSMA/CD).The Ethernet protocol is a so-called fair protocol, i.e. when there iscompeting access, all the terminals connected to a bus have, on astatistical average, the same chance of transmitting via the bus theirdata which is to be transmitted, regardless of the type of data to betransmitted.

However, in many cases it is necessary to prefer certain data flows overothers. Examples of this are data streams with real-time requirements,for example a sound data stream or a video data stream, but also alarmmessages for controlling machines. Such data streams require a certainminimum quality during their transmission. Guarantees for such minimumquality levels are, however, currently not ensured with the Ethernetprotocol, since with the CSMA/CD protocol it is not possible to make adistinction between data streams and therefore different treatment ofdata streams is also impossible.

The Ethernet bus is a passive transmission medium and the switching workis distributed between the terminals which also operate according to theEthernet protocol. The so-called Switched Ethernet is a technology inwhich local networks according to the IEEE 802.3 Standard are coupled bymeans of packet switching instead of the otherwise customary Ethernetbus. Packet switching is implemented by means of the so-called Ethernetnode. An Ethernet node has a plurality of bidirectional accesses, theso-called ports. The Ethernet node must pass on incoming data packetsthrough at least one output port which is coupled directly or indirectlyto the destination or destinations of the data packet. If differentinput packets are received and have to be output via the same outputport, the packets are buffered. The buffer used for this can overflow incases of high load and newly arriving data packets are lost in thiscase.

Various packet formats of the Ethernet protocol are known from thefollowing document, U.O. Pabrai, UNIX Internetworking, Artech House,Boston, London, page 23, 1993.

The invention is based on the problem of specifying a method which iscompatible with the Ethernet Standard and with which a certain minimumquality of the transmission for data streams is ensured with respect toreal-time requirements for the transmission.

In the method according to the present invention, at least one timingmessage is generated by a first arrangement at predefinable timeintervals and is transmitted to at least one second arrangement. Thetiming message contains a synchronization message, as a function ofwhich the time intervals which are provided for the transmission of datapackets (DP) each having a predefinable priority class are determined.After reception of the timing message, the received timing message isevaluated, a synchronization time being determined, as a function ofwhich the time intervals which are provided for the transmission of datapackets each having a predefinable priority class, are determined.

By means of this method, it becomes possible to reserve during theentire communications connection the resources which are assigned to apredefinable communications connection, are exchanged in acommunications setup phase and are required during the communicationsconnection. In this way, considerably more secure guarantees for thequality requirement of the data packets to be transmitted can befulfilled.

Advantageous developments of the present invention are as follows

In one development of the method it is advantageous to assign a priorityclass to each data packet to be transmitted by a first arrangement, andto mark the data packet according to the priority class. Then, the datapacket is transmitted to a second arrangement taking into account thepriority class.

A considerable advantage of this development is especially the fact thatit is possible to prioritize the data packets, for example depending onthe type of the data stream to be transmitted. In this way, it ispossible, on a statistical average, to ensure the required quality fordata packets which require a higher priority because of qualityrequirements relating to real-time requirements during transmission.

The expression “on a statistical average” is to be understood in thiscontext to mean that it is possible to ensure the quality requirementswith a certain degree of probability according to the priority classused. The cause of this that the data packets are transmitted accordingto their priority, for example data packets with a relatively highpriority are preferred over data packets with a relatively low priority.

In order to be able to implement a multi-stage communicationsconnection, i.e. a communications connection via several Ethernetswitching nodes, it is advantageous in one development of the inventionthat the data packet is received from a second arrangement, the priorityclass assigned to the data packet is determined and in the case ofwhich, in turn, the data packet is transmitted on taking into accountthe priority class.

By means of this procedure, the method is simplified since an entirelynew priority class for the data packet does not, in turn, have to beformed in each switching node and assigned to the data packet, rathermerely the priority class which has previously been assigned to the datapacket is determined, and the priority class continues to be used in therest of the method.

In order to assign the priority class to the data packet it isadvantageous to analyze information contained in the data packet fed tothe so-called Ethernet layer and relating to the type of the data packetand thus to the type of the communications connection or else to thetype of the data stream, and to take into account the analyzedinformation in the assignment of the priority class. In this way, itbecomes possible automatically to analyze and to ensure the type of thedata packet, and thus the quality requirements of the data stream.

In addition, in one development of the invention it is advantageous tocarry out an access check for the data packet, as a result of which itis possible to prevent the arrangement with which the method is carriedout from being overloaded as a result of an excessive number of datapackets to be transmitted.

In addition, in one development of the invention it is advantageous todivide up a buffer of the arrangement into a plurality of parts and toassign each part of the buffer to at least one priority class in eachcase. This means that in each case only data packets of thecorresponding priority class can be stored in the corresponding part ofthe buffer.

The development described above is improved even more by virtue of thefact that the data packets are output from the corresponding parts ofthe buffer and transmitted in a predefinable sequence. The sequence canbe predefined according to any desired scheduling method.

In addition it is advantageous that, in the event of the buffer memory,or part of the buffer memory in an arrangement which is configured as anEthernet switching element, overflowing, the data packet causing theoverflow is rejected only if it is not possible to abort the receptionprocedure by means of an artificial collision for this data packet.

In addition, in one development it is advantageous to generate theartificial collisions of the data packets only for data packets forwhose source arrangement the generation of an artificial collision isknown to be permissible, i.e. can be processed by the transmittingarrangement, for example. This development makes a selection for thearrangements which can process an artificial collision of a transmitteddata packet.

BRIEF DESCRIPTION OF THE DRAWINGS

The features of the present invention which are believed to be novel,are set forth with particularity in the appended claims. The invention,together with further objects and advantages, may best be understood byreference to the following description taken in conjunction with theaccompanying drawings, in the several Figures of which like referencenumerals identify like elements, and in which:

FIG. 1 shows a diagram of arrangements of a communications connectionwith two terminals and a switching unit, which exchange data packetsaccording to the Ethernet protocol;

FIG. 2 shows a flowchart in which developments of the method areillustrated;

FIGS. 3a to 3 f show a diagram in which various protocol formats of theEthernet Standard, and various associated possible ways of marking adata packet are illustrated;

FIG. 4 shows a diagram of the arrangement, with a number of furtherdevelopments and detailed illustrations with which the interaction withfurther communications layers is described;

FIGS. 5a to 5 f show various protocol formats and associated possibleways of implementing a back-pressure method (described below) incompliance with the Ethernet Standard;

FIG. 6 shows a message flowchart in which, by way of example, asignaling operation and the exchange of data of the arrangementsillustrated in FIG. 1 is described;

FIG. 7 shows a diagram in which a chronological division of thebandwidth of the communications connection into a plurality of timeintervals for various priority classes is illustrated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates arrangements of a communications connection(illustrated by way of example), in which data packets are transmittedaccording to the Ethernet Standard.

A first arrangement A1, a second arrangement A2 and further arrangementsAi are illustrated.

In this exemplary case, the first arrangement A1 is embodied as anEthernet terminal. The second arrangement A2 is embodied as a switchingelement, as a so-called Ethernet switching node (Ethernet switch). Afurther arrangement Ai is in turn configured in this exemplary case asan Ethernet terminal. Each further arrangement Ai is unambiguouslymarked with a first index i, the first index i being any desired naturalnumber.

Between the arrangements A1, A2, Ai there is a point-to-pointconnection, through a first coupling K1 between the first arrangement A1and the second arrangement A2, and a second coupling K2 between thesecond arrangement A2 and the further arrangement Ai.

However, it is also possible for arrangements which are configured asEthernet terminals to be coupled directly to one another in theso-called shared Ethernet, and not separated by means of at least onearrangement configured as a switching element, as in the so-calledswitched Ethernet.

Since the Ethernet Standard is oriented according to the so-called layermodel of the International Standardization Organization (ISO), thearrangements in the main illustration are described in the form ofcommunication layers. The couplings K1, K2 form the physical medium,together with the so-called physical layer PHY, which may also bereferred to as a bit transmission layer. The Ethernet layer, for examplethe layer of Media-Access Control (MAC layer) is coupled to the bittransmission layer. The standardized Ethernet protocol is carried out inthe Ethernet layer. Developments of the method can be consideredlogically as an intermediate layer between the MAC layer and further,higher communications layers. For this reason, in FIG. 1, the method isillustrated as an independent layer RMAC (Real Time Media-AccessControl).

The independent layer RMAC designated below as intermediate layer RMACis, on the one hand, coupled to the MAC layer and, on the other hand,coupled to further communications layers. Further communications layersare to be understood as any desired, known transportation protocols, forexample TCP/IP (Transport Control Protocol/Internet Protocol) or UDP/IP(User Datagramm Protocol/Internet Protocol) or IPX, etc. All thecommunications layers which are arranged logically above theintermediate layer RMAC are referred to in their totality in FIG. 1 ashigher layers HL for sake of simplicity. The general structure of thearrangements relating to the higher layers HL and of the bittransmission layer PHY and the MAC layer can be as desired within thescope of the respective protocol being used. Since the secondarrangement in this exemplary case is configured as an Ethernet switch,the second arrangement does not have any higher layers HL in this case.This is not necessary according to the Ethernet Standard.

Even if only three arrangements are illustrated in FIG. 1, acommunications connection in which the method is carried out can extendover any desired number of arrangements since the Ethernet protocolrelates only to a connection of arrangements which are directly coupledto one another.

Signaling

Possible signaling for the communications connection, in the form inwhich it is illustrated, for example, in FIG. 1, is described in FIG. 6.

A connection request (Connect Request) is transmitted to the secondarrangement A2 from the first arrangement A1. The Connect Requestcontains, for example, the target address DA, the transmitter addressSA, the flow identifier statement FID, the field type as well as aparameter field TSpec in which it is stated which quality features arerequested for the communications connection, as well as, for example, aservice class field RSpec, in which it is indicated which service class,for example, which priority class PKi is requested for thecommunications connection.

The Connect Request is passed on directly to the further arrangement Aifrom the second arrangement A2. In the case of a communicationsconnection which is routed via a plurality of Ethernet switching units,the second arrangement A2 is to be understood as a quantity of switchingunits which each pass on the Connect Request and the correspondingfurther data packets DP to that terminal which constitutes thecorresponding terminal for the communications connection.

The terminal, for example the further arrangement Ai, transmits aConnect Reply which, in addition to the target address field DA, thetransmitter address SA and the flow identifier FID, contains a Result(Success) statement, in which it is stated whether or not the requestedcommunications connection has been accepted.

In addition, in a Reason result statement it is stated why thecommunications connection has, for example, not been accepted. A causeof this can, for example, be an excessively low available bandwidth inthe communications network. These statements can be coded in apredefinable way, and these fields thus contain only random numericalvalues.

The Connect Reply response is passed onto the first arrangement A1 via“all the second arrangements” A2. After the reception of the ConnectReply response in the first arrangement A1 and of a positive response,i.e. a response to the effect that the communications connection hasbeen accepted, this connection setup phase described above isterminated.

This is followed by the actual transmission of the useful data, that isto say of the data packets DP to which in each case there is assignedaccording, for example, to the negotiated priority class PKi or even afreely predefinable priority class PKi which can be defined by thetransmission, or else which are in each case assigned adaptively to thedata packet DP, for example as a function of the network loading of therespective Ethernet switching arrangement.

If a communications connection is aborted, this is achieved, forexample, by virtue of the fact that a connection abort request(Disconnect Request) is transmitted to the second arrangement A2 by atransmitter, for example the first arrangement A1, and is passed on fromthe second arrangement A2 to the further arrangement Ai. The connectionabort request Disconnect Request contains, for example, the targetaddress DA, the transmitter address SA and the flow identifier FID.

Implementing the Priority-controlled Transmission at the BitTransmission Layer

In the method there is provision for the bandwidth which is available,in each case, for example in the Ethernet or else for a communicationsconnection within the scope of the Ethernet, is divided into a pluralityof bandwidth areas, for example corresponding to the number of priorityclasses PKi provided.

Each part of the bandwidth serves to transmit the data packets DP whichare assigned to the priority class PKi to which the respective part ofthe bandwidth is also assigned.

For the sake of simpler illustration, the quite simple case in whichonly two priority classes PK0 and PK1 are provided (cf. FIG. 7) isdescribed below. However, this does not in any way restrict the generalapplicability of this method for any desired number of priority classesand thus to any desired number of time slots.

For this case, for example, two time slots, a first time slot ZS1 and asecond time slot ZS2, are provided. The first time slot ZS1 is, forexample, for high-priority data, that is to say for data packets DP towhich the second priority class PK1 has been assigned, and the secondtime slot ZS2 is provided for data packets to which the low priorityclass PK0 has been assigned.

Here, there is provision, in a development of the method, to simplifythe method in such a way that only the magnitude of the first time slotZS1 is administered. This means that it is advantageous for the timeslots ZS1, ZS2 to be of variable configuration in terms of their width.Starting out from a freely predefinable reference time t₀, a startingtime of the second time slot ZS2 is obtained from the sum of thereference time t₀ and a time slot length S1 of the first time slot ZS1.

The time slot length S1 is selected in such a way that offered trafficA_(H) of all the high-priority data streams can be transmitted. Thefollowing applies: $A_{H} < {\frac{S1}{S_{F}} \cdot B}$

B designates the bandwidth of the corresponding Ethernet segment. S_(F)designates the sum of the time slot length S1 of the first time slot anda time slot length S2 of the second time slot ZS2 (S_(F)=S1+S2). Theabove rule gives only a rough guide to the dimensioning of the firsttime slot length S1. Any desired rule for dimensioning, i.e. dividing upof the individual time slot lengths is known to the person skilled inthe art.

If there are requests for the maximum delays T_(Dmax) of the data whichare to be transmitted with high priority, the following rule, forexample, is to be complied with:

S_(F)<min T_(dmax)+S1

(all the high-priority communications connections)

In one development of the method it is advantageous to synchronize thereference time t₀ of a freely predefinable arrangement, for example bymeans of timing messages at freely predefinable time intervals, i.e. thereference time t₀ is transmitted to all the other arrangements by anarrangement in freely predefinable time intervals. The timing message isreceived by the arrangements and used as their new reference time t₀.Genuine synchronization of the arrangements is not possible in theEthernet. However, this periodic freshening up of the reference times t₀permits sufficiently precise coordination of the clocks contained in theoperating systems of the arrangements.

The standardized Ethernet protocol also has, in particular, thedisadvantage that, as a result of the free access, in accordance withthe CSMA/CD protocol, of all the equipment connected to the Ethernetbus, free access is possible for all the data packets DP to betransmitted, irrespective of the type of data to be transmitted.

The result of this is that for data streams which make predefinablereal-time requests relating to the transmission of the data packets DPof the corresponding communications connection, [lacuna] cannot beensured.

The various real-time requests are referred to below as qualityfeatures. Quality features are to be understood, within the scope ofthis document, as, for example, the following criteria:

delay times of the data packets DP,

delay time fluctuations in the data packets DP,

losses of the data packets DP given overloading of the communicationsconnection or of the arrangements,

useful data rates, etc.

In order to be able to ensure specific quality features which arecompletely application-specific and can be freely predefined in anapplication-specific fashion, the method has, in an advantageousdevelopment, the following method steps which are illustrated in FIG. 2.

The data packet DP to be transmitted is fed to the intermediate levelRMAC by a higher level HL. In order to transmit the data packet DP inthe Ethernet, the following method steps are provided in thisdevelopment.

In a first step 201, the data packet DP is assigned a priority class PKjfrom a quantity of any desired number of priority classes PKj. Eachpriority class PKj is unambiguously marked with the second index j, thesecond index j being any desired natural number.

In a further step 202, the data packet DP is unambiguously marked inaccordance with the priority class PKj.

In a last step 203, the data packet DP is transmitted by the firstarrangement A1, in which the method is being carried out, to the secondarrangement A2.

In one development of the method, further method steps are providedwhich are also illustrated in FIG. 2.

In a further method step 204, the data packet DP is received by thesecond arrangement A2.

Then, in the second arrangement A2, the priority class PKj which hasbeen assigned to the data packet DP in the first arrangement A1 isdetermined 205.

Taking into account the priority class PKj which has been determined,the data packet DP is transmitted on 206, in this exemplary case whichis illustrated in FIG. 1, to the further arrangement Ai.

The concrete embodiment of the individual method steps in this exemplaryembodiment will be explained in more detail below.

Assignment of the Priority Class PKj to the Data Packet DP 201

Generally, the assignment of the priority class PKj to the data packetDP signifies a mapping of the possibly large number of required qualityfeatures onto the priority class PKj, by means of which thecorresponding combination of necessary quality features is ensured.

Even if the number and properties of the quality features are random, ithas proven advantageous to take into account the following quality ofservice parameters (QOS parameters) in order to ensure the qualityfeatures in the method. It has proven sufficient for the following fourpriority classes PKj (j=0, 1, 2, 3) to be taken into account within thescope of this method.

A first priority class PK0 is provided for a connectionlesscommunications connection in which all that is assured is that therespective data packet DP is transmitted, with an unspecified bit rate,as well as possible depending on the utilization rate of thecommunications network without anything being ensured and without aconnection setup. Thus, the first priority class PK0 corresponds to thelowest priority which can be assigned to the data packet DP.

A second priority class PK1 is provided for a connection-orientatedcommunications connection in which a controlled delay, i.e. a maximumdelay of the transmission of the data packet DP, is ensuredstatistically. In the so-called controlled delay service, the followingfeatures, for example, are implemented:

a bandwidth which is required for the connection and which is negotiatedin a further described connection setup is ensured;

the average delays during the transmission of the data packet DP whenthere is a high degree of loading of the communications network are inno way worse than the delays of the data packet DP to which the firstpriority class PK0 has been assigned;

the maximum delay in the transmission of the data packet DP with a highdegree of loading of the communications network is considerably lowerthan that of data packets DP of the first priority class PK0;

the loss rate of the data packets DP owing to overflowing of the buffermemory PS of the arrangements A1, A2, Ai is not considerable as long asthe properties of the data stream, that is to say of the communicationconnection negotiated in the “traffic contract” negotiated in theconnection setup phase, for the respective communications connection aremaintained.

With the second priority class PK1, a service is thus implemented withwhich a bandwidth demand with few real-time requirements, or with noneat all, is ensured. The second priority class PK1 is suitable, forexample, for burst-type traffic with a demand for a communicationsconnection for a specific bandwidth.

A third priority class PK2 relates to a connection-orientatedcommunications connection. The following services, for example areprovided for data packets DP to which the third priority class PK2 hasbeen assigned:

most data packets DP are actually transmitted completely;

in most cases, the delay of the data packets DP during the transmissionwill not exceed a predefinable maximum delay time for the transmissionof the data packets DP.

In this context, the expression “most data packets” is to be understoodsuch that it is a predefinable number which is to be stated, forexample, in the connection setup phase. It is, for example, sufficientin many cases that one of 1000 transmitted data packets DP within asecond and at maximum one of 10,000 data packets DP in even longer timeintervals would exceed the limit given by the value for “most datapackets”. Thus, the third priority class PK2 will ensure a service inwhich a controlled delay plus a maximum delay limit is ensured, thusimplementing an “quasi-real-time” service.

A fourth priority class PK3 is also provided for a connection-orientatedcommunications connection. In the fourth priority class PK3 whichcorresponds to the highest priority which can be assigned to the datapacket DP, the following services, for example are ensured:

the bandwidth, for example, which is required for the communicationsconnection and which is negotiated during the connection setup is madeavailable;

predefinable maximum delay times for the data packet DP are guaranteedduring the transmission;

no losses of data packets DP occur owing to overflowing of the bufferPS.

Thus, the communications-connection parameters in the fourth priorityclass PK3 which are negotiated during the connection setup are ensuredwith a very much higher degree of statistical reliability than in thecase of the other priority classes PK0, PK1, PK2 as long as the entirecommunications network does not collapse, for example owing to a faultin the communications network.

Marking of the Data Packet DP According to the Assigned Priority ClassPKi 202.

The method of marking the data packet DP so that the receiver of thedata packet DP can in each case determine which priority class PKi hasbeen assigned to the data packet DP can be carried out in various ways.

A customary Ethernet data packet DP has, for example, the followingfields in the data packet DP which are mentioned in the EthernetStandard (cf. FIG. 3a):

a destination address field DA in which the address of the receiver ofthe data packet DP is stated;

a transmitter address field SA in which the address of the transmitterof the data packet DP is stated;

a field type which is interpreted by the receiver of the data packet DPas an integer and is usually of the length of two octets. The field typeis interpreted differently depending on the number in the field. If thenumber is smaller than 1500, the field type is interpreted, for example,as a long field, and the rest of the data packet DP corresponds to thecustomary so-called logic-link control format (LLC format). If thenumber in the field type is, however, not smaller than 1500, the numberis interpreted as a type statement. The type statement contains a codefor the network protocol which has generated the following informationcontained in the data packet DP.

In the so-called LLC format, the network protocol is defined by theso-called service access point (SAP), the LLC service access point (LLCSAP). An example of such a packet format is illustrated in FIG. 3c. FIG.3e illustrates a variant of the LLC format, the so-called LLC subnetattachment point format (SNAP) in which the service access point (SAP)is set permanently to the value hexadecimal 0A. The network protocol iscoded in a separate field type in this variant (cf. FIG. 3e).

In addition, all the protocol elements have an information field Infocontaining the actual information in the data packet DP which has beensupplied by higher layers HL and is to be transmitted.

Also, a fault detection field FCS with a check sum code in the protocolformats is provided.

The marking of the data packet DP with the priority class KPi assignedto the data packet DP can be carried out in different ways depending onthe respective protocol format.

In FIG. 3b, a priority mark PM is entered in the field type for thecustomary protocol format from FIG. 3a. The priority mark PM is anunambiguous value with which the priority class PKi is unambiguouslyindicated. This value must generally be reserved unambiguously for thecorresponding priority class.

In addition, there is provision in one variant of the method for datapackets DP with the lowest priority, that is to say for example of thefirst priority class PK0, not to be marked at all but rather to be usedwithout modification in accordance with the customary Ethernet Standard.

Since it is possible for an arrangement to operate with layers HL ofdifferent levels, for example both with the TCP/IP protocol, on the onehand, and also with the SPX/IPX protocol, on the other, for differentcommunications connections it is, in one development of the method,advantageous to provide a further field in the data packet DP. Thefurther field is referred to as a flow identifier FID. The flowidentifier FID is unambiguously generated in the arrangementtransmitting the data packet DP. Thus, it is possible for the receiverof the data packet DP to determine, with reference to the data packetDP, an unambiguous assignment of the data packet DP to the type of thecommunications connection, the priority mark PM and the Service AccessPoint, and of the coupling to the higher layers. This is possible since,as a result of the procedure described above, the combination of the MACtransmitter address and of the flow identifier FID is unambiguousworldwide, and can thus be used for unambiguous assignment of the datapacket DP in the receiver of the data packet DP.

Since, as has been described above, in the case of marked data packetsDP the original field content of the field type is described, theinformation which is contained therein relating to the associatednetwork protocol must previously be transmitted separately to thereceiver, for example to the second arrangement A2. This takes place ina signaling phase which is explained in more detail below.

The marking for the protocol format which is described in FIG. 3c isillustrated in FIG. 3d. Here, the priority mark PM is contained in thefield DSAP which usually contains the receiver service access point ofthe higher layer HL.

In addition, the priority mark PM can also be contained, instead oradditionally in a field SSAP which usually contains the value of theservice access point of the higher layer HL of the transmitter of thedata packet DP.

In this variant, the field of the flow identifier FID is, in onedevelopment, likewise additionally provided in the data packet DP.

In the format which is illustrated in FIG. 3e, the priority mark PM is,for example, transmitted in the field type (cf. FIG. 3f). In addition,there is, in turn, a field provided for the flow identifier FID. Thispossibility of converting the priority mark PM, and thus the statementof the priority class PKi, into a marking of the data packet DPconstitutes merely one of a large number of examples.

In variants, it is likewise possible to provide new fields for receivingthis information.

If different service access points are used for different data streams,the assignment of the data stream to the priority class PKi is writteninto a table, and each data packet DP which is assigned to the datastream is assigned the corresponding priority class PKi which has beendefined in the table.

If, however, it is not the case that a separate access point is providedfor each data stream, there is provision to determine the identificationnumber of the port of the data packet DP which has been supplied by aTCP/IP layer. However, other information which identifies the datastream to which the data packet DP is assigned, and which has alreadybeen generated in higher layers than, for example, the TCP/IP layer, canalso be identified and evaluated.

The result of this is, for example, that in the event that it waspossible to identify the associated data stream for the data packet DP,it is possible to perform a mapping onto the corresponding priorityclass PKi which is to be assigned to the data packet DP.

In one development of the method there is, in addition, provision forthe mapping of the quality features which are to be ensured for the datastream, that is to say the communications connection, to be designed soas to be dynamically configurable during a connection setup phase. If noconnection setup phase has been carried out for the datastream to whichthe data packet DP is assigned, in the simplest case the data packet DPis correspondingly assigned the first priority class PK0.

The arrangement and the method are explained in more detail by means ofthe following example. The transport protocol used by any desiredapplication ANW (cf. FIG. 4), for example any desired program, uses theUDP/IP protocol in order to transmit video data over the Ethernet.

If the port number of the UDP data stream to be transmitted is known, itis possible for resources to be requested for the connections. Here, fora signaling operation which is described below, a resourceadministration unit BMV determines which resources are required forwhich UDP port number.

The resource administration unit BMV carries out, for example, aconnection setup phase and marks the new communications connectionunambiguously. The marking is detected by the arrangement in that, forexample, the UDP port number is evaluated, and, based on this number,the communications connection for the data packet DP and thecorresponding priority class PKi can be determined.

FIG. 4 illustrates the arrangement with which the method can, by way ofexample, be carried out. The arrangement, for example the firstarrangement A1, the second arrangement A2 and the further arrangement A1has at least one data packet classification unit DK, one prioritymarking unit PME and a buffer PS.

The arrangement is logically arranged between the higher layers HL andthe MAC layer.

The data-packet classification unit DK is configured in such a way thatthe mapping of the quality features onto priority classes PKi describedabove can be carried out.

The priority marking unit PME is configured in such a way that themarking described above, for example therefore the writing of predefinedvalues into specific, predefinable data fields of the data packet DP, iscarried out.

The data packet DP to be transmitted is supplied by the higher layers HLof the arrangement. Here, it is fed to the data-packet classificationunit DK, which determines the priority class PKi for the data packet DPand the data packet DP is stored in the buffer PS.

In a further development of the method there is provision to assignseparate parts of the buffer PS of a predefinable magnitude to theindividual priority classes PKi. Only the data packets DP to which thepriority classes PKi which correspond to the part of the buffer PS hasbeen assigned are written in each case into the separate parts which areassigned to the priority classes PKi. The individual parts of the bufferPS are preferably configured according to the First-In-First-Outprinciple (FIFO buffer). In this way, it is easily possible to implementa so-called queue for the data packets DP before the transmission of thedata packets DP.

A simple way of implementing the method is made possible by means ofthis refinement of the arrangement.

Any desired scheduling method can be used to read out the data packetsDP from the parts of the buffer PS. An overview of the variousscheduling methods is given in the following document, H. Zhang and D.Ferrari, Rate-Controlled Static-Priority Queuing, Proc. Of INFOCOM '93,San Francisco, Calif., April 1993.

A very simple algorithm for reading out the data packets DP from theparts of the buffer PS can take the form in which whenever a data packetDP is to be read out of the buffer PS for the transmission of the datapacket DP, in each case that part of the buffer PS which corresponds tothe highest priority class, for example to the fourth priority classPK3, is examined and checked to determine whether a data packet DP iswaiting for transmission in this part of the buffer PS. If this is notthe case, in succession and in descending order of priority, the nextpart of the buffer PS to which the next lowest priority class PKi−1 isrespectively assigned is correspondingly searched for. In onedevelopment of the arrangement, a scheduler unit SCH is provided forcarrying out the appropriate scheduling method.

In one development of the arrangement, the resource administration unitBMV is additionally provided.

The resource administration unit BMV is configured in such a way that atleast one of the following functions is ensured by the resourceadministration unit BMV:

the resources of the respective arrangement A1, A2, Ai and/or resourcesof a communications network used for transmitting the data packet DP areadministered, these being, for example, the buffer PS, the bandwidth ofthe Ethernet, which is to be reserved, for example, for a communicationsconnection, the scheduler SCH, etc.;

for the data packet DP, an access control is carried out as a functionof which it is determined whether or not the data packet DP is furtherprocessed;

a signaling operation is carried out between the arrangement and atleast one further arrangement with which the arrangement is connected.In this signaling operation, no characteristics of the communicationsconnection, for example the reserved required bandwidth and furtherquality features for the communications connection which are ensured forthe communications connection to which the respective data packet DP isassigned are defined.

In one development of the arrangement it is advantageous to assign aseparate, independent Media-Access-Control address (MAC address) to theresource administration unit BMV. As a result, it becomes possible toimplement the resource administration unit independently, onlyphysically connected, of the rest of the arrangement and to communicatewith the arrangement only via couplings.

Generation of Artificial Collisions

In one development of the method there is provision, in an arrangementconfigured as an Ethernet switch, to generate, in the event that thebuffer PS or a part of the buffer PS is full and a data packet DP is tobe written into the buffer PS or into the filled part of the buffer PS,a so-called artificial collision for the data packet DP to be writtenin, as a result of which the transmitter is directly informed that thedata packet DP cannot be processed at the respective time.

The transmitter of the data packet DP subsequently aborts thetransmission of the data packet DP and the transmission attempt of thedata packet DP is not repeated until after a randomly selected timeperiod. This prevents data packets DP being lost since the transmitterof the data packet DP completely transmits the data packet DP once more.

However, since in this development of the method, the propagation timesfor the data packet DP increase by the amount of the time up to thefirst successful transmission attempt of the data packet DP specificallynot only for the data of the communications connections which have topass through the filled buffer PS but also for all the data packets DPof the braked, i.e. “blocked” transmitter, irrespective of thedestination of these data packets DP or of which communicationsconnection these data packets DP belong to, it is advantageous toprovide the following development.

However, in the case of data to be transmitted with, for examplereal-time requirements, excessively long delays are, as has beendescribed above, not acceptable under certain circumstances. For thisreason, it is advantageous to protect transmitters with suchrequirements against artificially generated, undesired collisions of thedata packets DP, since it is often more acceptable, with these types ofdata streams, to accept packet losses which are caused by theoverflowing of the buffer PS and/or of the part of the buffer PS than toaccept blocking of the entire network interface of the transmitter.

This problem is solved in that the use of the generation of artificialcollisions, which is referred to below as backpressure, is permitted, orprohibited, to terminals in a specific and dynamic fashion.

For this purpose, automatic assignment of the statement whether or notthe backpressure method is permitted for the respective terminal whichis identified by means of the MAC address is implemented. For thisreason, it is necessary for the receiver which is configured, forexample, as an Ethernet switch, of the data packet DP to be able todetect whether or not the transmitter of the data packet DP isauthorized for a backpressure method. This information can be contained,for example, in the packet format which is illustrated in FIGS. 5a to 5f and/or can be entered in a table in the receiver of the data packetDP, in each case in a terminal-specific fashion.

The packet formats (illustrated in FIGS. 3a, 3 c and 3 e) for anEthernet data packet DP are illustrated in FIGS. 5a, 5 c and 5 e.

In this development of the method there is provided, for example in thefield type, a status statement BPSTAT with which it is stated whether ornot the backpressure method is authorized for the transmitter of thedata packet DP.

Likewise, a flow identifier field FID is provided in one development(cf. FIGS. 5b, 5 e, 5 f). Even if the same fields have been used in thisexemplary embodiment, as was described for the priority classes PKi,there is, however, likewise provision in one variant for further fieldsto be provided in the protocol format, in order thus to be able totransmit both types of information in one data packet DP.

The invention is not limited to the particular details of the methoddepicted and other modifications and applications are contemplated.Certain other changes may be made in the above described method withoutdeparting from the true spirit and scope of the invention hereininvolved. It is intended, therefore, that the subject matter in theabove depiction shall be interpreted as illustrative and not in alimiting sense.

What is claimed is:
 1. A method for transmitting data packets withpredefinable priority classes in a network from a first arrangement toat least one second arrangement, comprising: generating at least onetiming message by the first arrangement at predefinable time intervalsand transmitting the at least one timing message to at least the secondarrangement which is coupled to the first arrangement; determiningtiming intervals as a function of a synchronization message in the atleast one timing message, the timing intervals being provided fortransmitting data packets each with a predefinable priority class;receiving the timing message by the at least one second arrangement;evaluating the received timing message, a synchronization time beingdetermined as a function of which the timing intervals, which areprovided for the transmission of data packets each having a predefinablepriority class, are determined; and reserving, for a communicationsconnection which has any desired number of data packets to betransmitted, predefinable resources for the communications connection ata beginning of the communications connection as a function of the timeintervals.
 2. The method as claimed in claim 1, wherein a data packet istransmitted only in a time interval which is provided for a priorityclass which has been assigned to the data packet.
 3. The method asclaimed in claim 1, wherein a respective data packet to be transmittedis assigned one of at least two priority classes, wherein the respectivedata packet is unambiguously marked according to the priority class, andwherein the respective data packet is transmitted to the secondarrangement taking into account the priority class assigned to the datapacket.
 4. The method as claimed in claim 3, wherein the respective datapacket is received by the second arrangement, wherein the priority classassigned to the respective data packet is determined, and wherein therespective data packet is further transmitted taking into account thepriority class assigned to the data packet.
 5. The method as claimed inclaim 3, wherein information contained in the respective data packetrelating to at least one of a type of data packet and a communicationsconnection to which the data packet is assigned, is analyzed, andwherein the assignment of the priority class is made taking into accountthe information.
 6. The method as claimed in claim 1, wherein an accesscheck is carried out for at least one data packet.
 7. The method asclaimed in claim 1, wherein signaling relating to a communicationsconnection to which a respective data packet is assigned is carried outbetween the first and second arrangements with which the method iscarried out and which are connected to one another, before thetransmission of the respective data packet takes place.
 8. The method asclaimed in claim 3, wherein at least each priority class is assigned atleast a part of a buffer, and wherein the respective data packet isstored only in the part of the buffer which is assigned to a priorityclass which was also assigned to the respective data packet.
 9. Themethod as claimed in claim 8, wherein at least one of a number of storeddata packets in the buffer and a number of stored data packets at leastin a part of the buffer is determined, the part of the buffer beingassigned to a priority class, and wherein only a data packet is storedwhich has a corresponding priority class with which the data packetsstored in the buffer are output and transmitted in a predefinablesequence.
 10. The method as claimed in claim 9, wherein a sequence isdefined by the priority classes such that the data packets in thesequence are output and transmitted according to decreasing priority ofthe data packets.
 11. The method as claimed in claim 9, wherein thesequence is defined by a predefinable scheduling method.
 12. The methodas claimed in claim 8, wherein when the buffer or at least a part of thebuffer is completely filled with stored data packets which have not yetbeen read out, and when a further data packet to be transmitted is to bestored in the buffer or at least in the part of the buffer, anartificial collision is generated and information regarding theartificial collision is conveyed to the arrangement transmitting thedata packet.
 13. The method as claimed in claim 12, wherein anartificial collision is generated only if the data packet containsinformation that the generation of an artificial collision is permittedfor the arrangement transmitting the data packet.